The goal is to gain new insights into the function of the incertohypothalamic A13 dopamine (DA) cell group. We will achieve this goal by using a multidisciplinary approach to (1) determine whether the A13 DA nucleus is sexually dimorphic. We will use a state-of-the-art computer graphic system to count the tyrosine hydroxylase (TH) labelled cells. In microspectrofluorometric studies, only DA spectra is observed from this region. Thus we can say with reasonable accuracy that TH labelled cells are indeed DA cells. We will plot these DA cells in 3-dimensional space of the nucleus in both male and female rats. This will indicate if there are any differences in DA cell number and if so, where in the 3-dimensional space of the nucleus do these differences lie; (2) define the efferent projections of this cell group. We will use an orthograde tracer, lectin PHA-L, combined with TH immunocytochemistry to trace the neuronal pathways of A13 DA neurons in male and female rats; (3) localize the target areas of these A13 DA neurons. We will immunostain hypothalamic sections with luteinizing hormone releasing hormone (LHRH) and TH antisera to determine the relationship between TH positive terminals and LHRH neurons in the anterior hypothalamic area/medial preoptic area (AHA/mPOA) in both groups of animals; (4) examine the electrophysiological and pharmacological properties of antidromically identified A13 neurons. We will use the techniques of extracellular single cell recordings and microiontophoresis to determine neuronal firing rates, firing patterns and autoreceptor sensitivities of putative A13 DA neurons in the male rat, and female rat under high and low levels of circulating oestradiol; and (5) determine the role of these neurons in the release of LH from the anterior pituitary gland. We will electrically stimulate the A13 DA region and measure LHRH levels in hypophyseal portal vessels and LH levels in systemic blood in both groups of animals. It is hoped that these basic experiments will shed light on the basic properties of A13 DA neurons and in so doing lead to a better understanding of the role of hypothalamic DA in the regulation of LH release from the pituitary gland in both male and female rats.